Anti-folate (Trimethoprim & Sulphamethoxazole)

Question 1

1st step of folate synthesis inhibited by SMX & enzyme inhibited

Answer 1

• PABA analogue

- blocks dihydrofolate synthase

Question 2

2nd step of folate synthesis inhibited by TMP & enzyme inhibited

Answer 2

dihydrofolate reductase

Question 3

difference in strength of TMP & SMX when combined vs on their own

Answer 3

• on own –> bacteriostatic

- combined –> bacteriocidal

Question 4

gram -ve GI & urinary indications for antifolate abx

Answer 4

• UTI

- acute prostatitis

Question 5

gram +ve indication for antifolate abx

Answer 5

• MRSA

- nocardia

Question 6

when are antifolate agents prescribed as prophylaxis for pneumocystis jirovecii pneumonia (PJP)

Answer 6

CD4<200

Question 7

when are antifolate agents prescribed as prophylaxis for toxoplasmosis

Answer 7

CD4<100

Question 8

SEs anti-folate agents

Answer 8

• pancytopenia
• megaloblastic anaemia
• teratogen in 1st trimester (neural tube)

Question 9

sulfa drugs SEs

Answer 9

• sulfa allergy
• anaemia (haemolytic in enzyme G6PD deficiency)
• SJS
• type 4 renal tubular acidosis –> hyperkalaemia
• photosensitivity
• lupus

Question 10

interactions of sulfa drugs

Answer 10

inhibit c450

Question 11

contraindications of antifolate

Answer 11

• pregnancy

- blood dycrasias

Question 12

TMP mostly excreted via

Answer 12

urine